Week 2 Lecture 2 - natural selection Flashcards
Is evolution like a chain or a branch
branch
What is adaptation
function if a trait that has been evolved by NS
What are the 4 core principles of natural selection?
- variability
- heritability
- surplus offspring
- non-random survival and reproduction
What is variability?
- individuals of species differ, this gives NS something to act on
- variability can be so good that it becomes hard to determine what distinguishes a species
What is heritability?
variability has to be transmitted generation to generation (vertical transmission)
Where does the main source of heritable variability come from?
genes
Do genes blend?
no
What is surplus offspring?
more offspring produced than can be supported by the environment (carrying capacity)
What is non-random survival?
complexity could not have arose by chance
survival and reproduction isn’t random
individuals with traits better suited to the current env., on average, are more likely to survive and produce viable offspring
What are the 4 Fs of fitness?
- fighting
- feeding
- fleeing
- reproduction
What is fitness?
the differential survival reproduction of individuals
Do organisms always perfectly adapt to an env.?
no
the optimum solution can change –> getting from one to the other world would involve a reduction in fitness
What is genetic drift?
random change due to change
What factors can affect genetic drift?
- pop. bottleneck
- founder effects
What did Mendel do?
cross-breed peas to show that genes don’t blend
What is the law of segregation (Mendel’s 1st law)
every individual has 2 copies of the “particles” for a trait
pairs of these particles separate and get passed into different sex cells
they unite with another particle after fertilisation and form a zygote
What is the law of independent assortment (Mendel’s 2nd law)?
particles for different traits assort independently
Why do some traits appear to blend?
- there is more than 1 gene for the trait
- codominance
- incomplete dominance
What is locus?
genes occupy different positions on a chromosome
What are the different effects that genes can have on the phenotype?
- one gene, one effect
- polygenic: many genes one effect
- pleiotropic: one gene, many effects
- polygenic and pleiotropic
What do structural genes code for?
proteins
What is a gene?
a segment of DNA specifying the sequence of amino acids in a protein
What are 4 functions of proteins?
- structural functions e.g., collagen
- enzymes e.g., lactase
- hormones e.g., insulin
- regulatory proteins
What is epigentics?
non-genetic changes in gene expression
How can gene function be studied?
directly or indirectly
What are some examples of indirect gene study?
twin studies
What are some examples of direct gene study?
CRISPR, gene sequencing, SNP
What is neo-Darwinism?
fusion of Darwinian evolution by NS and Mendelian inheritance
What does Neo-Darwinism believe about evolution?
populations evolve not individuals
NS is one force for changing allele frequencies in populations. What are some others?
- mutation
- gene flow
- genetic drift (inc. founder effect)
- non-random mating (i.e., artificial selection)
- meiotic drive (selfish genes)
What is the selfish gene?
selection ultimately acts on genes not individuals
What is population genetics?
evolution to a population geneticist –> change in allele frequencies over time
What are analogies?
convergent evolution –> independent evolution produces analogous traits
traits that appear similar but evolved separately
What are homologies?
adaptive radiation –> similarity by descent
produces homologous traits
How can we tell is a trait is homologous or analogous?
comparative method –> phylogenetic history and similar ecological pressures
What are vestigial traits?
vestigial traits have lost their function through evolution
e.g., human fear or spiders
Are all traits adaptations?
no - not all origin stories are plausible
“Just so stories”
What are exaptations?
traits that serve a different purpose than the one they were adapted for
what are developmental byproducts?
traits that arise as a by-product for a selected trait somewhere else
What are maladptions?
traits can be adaptive in the env. in which they evolved, but not now
Can all traits endure phylogenetic inertia and genetic/physical constraints?
no
can evolvability be adaptive?
yes
